JP2753466B2 - Thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head, and more particularly, to a thermal head which can easily form a ground electrode and various signal conductor patterns on an insulating substrate of the thermal head. is there.

[0002]

2. Description of the Related Art An example of a conventional thermal head will be described with reference to FIG. Reference numeral 21 denotes a thermal head substrate on which an exothermic resistor 2
3, common electrode 24, individual electrode (not shown), connection terminal 2
5,. . . , 25 and drive ICs 26,. . . ,
26 is mounted. The heating resistor 23 and the common electrode 24 extend in the longitudinal direction of the insulating substrate 22, and the common electrode 24 commonly supplies electricity to the heating resistor 23.
Both ends of the common electrode 24 are connection terminals 24a, 24a.

The individual electrodes are individually energized to the heating resistors 23 and wire-bonded to the driving ICs 26, respectively. The drive IC 26 is also wire-bonded to the connection terminal 25. The connection terminals 25 are assigned to the respective driving ICs 26 by a predetermined number.
C26 are independently, for example, DI (data-in) D
It has signal connection terminals such as O (data out) and _VDD, and connection terminals to the ground electrode.

[0004] On the connection terminals 24a and 25, an edge 31a of a flexible substrate 31 is overlapped. A conductive pattern (not shown) is formed on the flexible substrate 31 so as to connect and conduct to each of the connection terminals 24a and 25. The flexible substrate 31 is reinforced by a reinforcing plate 32, and the reinforcing plate 32 includes a flexible substrate 3
A connector (not shown) for connecting 1 to the outside is attached.

[0005] The flexible substrate edge 31a is
The thermal head substrate 21 is formed by the silicone rubber 36 of FIG.
Is pressed against. The cover 35 includes screws 37,. . . ,
37 (only two at both ends are shown) and attached to the heat sink 30. These screws 37,. . . , 37 generate a pressure contact force between the flexible substrate edge 31a and the thermal head substrate 21. Also, this cover 35
Has a function of protecting the driving IC 26. 35a and 33 are insertion holes for screws 37, and 30a is a screw 3
Reference numeral 7 denotes a female screw hole to be screwed.

[0006]

In the above-mentioned conventional thermal head, various signal conductor patterns for the respective drive ICs 26 and connection terminals for the ground electrodes are formed for each location of the respective drive ICs 26. As a result, the number of various signal-system conductor patterns and ground electrodes formed on the upper surface of the insulating substrate 21 is extremely large. However, there is a problem that the cost required for forming the connection terminal is significantly increased.

Therefore, Japanese Patent Application Laid-Open No. Sho 62-3 is a prior art.
Japanese Patent Application Publication No. 2058 proposes that the number of ground electrodes be reduced by forming the ground electrodes in a line shape extending in parallel with each drive IC row near the other long side edge of the insulating substrate. ing. However, on the other hand, in this type of thermal head, the DI, D, D
O, LA (latch), CLK (clock) V _DD , STR
It is necessary to provide connection terminals for connecting external circuits to various signal system conductor patterns such as (strobe).
As in the prior art described above, the ground electrode is
In the case of a configuration in which it is formed in a line shape extending in parallel along the row of C, in order to provide a connection terminal for connecting an external circuit to the above-described various signal system conductor patterns near an edge of the insulating substrate, The connection terminal of the signal system is formed so as to three-dimensionally cross while being electrically insulated from the line-shaped ground electrode, or the line-shaped ground electrode is connected to the connection terminal of the signal system. It must be formed so that it crosses three-dimensionally in an electrically insulated state. In other words, the wiring pattern formed on the upper surface of the insulating substrate must have a two-layer structure. The cost required to form connection terminals for connecting external circuits to various signal-system conductor patterns and line-shaped ground electrodes was greatly increased.

It is a technical object of the present invention to provide a thermal head that solves these problems.

[0009]

In order to achieve this technical object, the present invention provides a method for forming a rectangular insulating substrate, which is formed near the edge of one of the long sides on the insulating substrate and parallel to the long side. A heating resistor, a common electrode formed between the one long side edge and the heating resistor and between both short sides on the insulating substrate, and commonly connected to the heating resistor, and formed on the insulating substrate; Individual electrodes for individually supplying current to the heating resistors, a plurality of drive circuit elements provided on the insulating substrate and connected to the individual electrodes, and connected to the respective drive circuit elements formed on the insulating substrate. In a thermal head including a ground electrode and various signal conductor patterns formed on the insulating substrate and connected to the drive circuit elements,
The ground electrode is formed in the vicinity of the other long side edge of the insulating substrate so as to extend in a line in parallel with the long side, and provided with a dividing part in the middle of the linear ground electrode, A connection terminal for connecting an external circuit to each of the various signal-system conductor patterns is formed so that each of the connection terminals extends to an edge of a long side of the insulating substrate. ".

[0010]

When the ground electrode for each drive circuit element is formed in the vicinity of the other long side edge of the insulating substrate so as to extend in a line parallel to the long side, the middle of the linear ground electrode is formed. And providing a connection terminal for connecting an external circuit to each of the various signal-system conductor patterns so that each of the connection terminals extends to an edge of a long side of the insulating substrate. Accordingly, connection terminals for connecting an external circuit to each of the various signal system conductor patterns are provided near the other long side edge of the insulating substrate without three-dimensional crossing while being electrically insulated from the ground electrode. Can be.

Therefore, according to the present invention, since the wiring pattern formed on the upper surface of the insulating substrate can have a single-layer structure, the connection terminals and the lines for connecting the external circuit to various signal conductor patterns are formed on the upper surface of the isolated substrate. This has the effect of significantly reducing the cost required to form the ground electrode.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In this figure,
The thermal head substrate 1 is formed by forming various conductor patterns on an insulating substrate 2 formed in a rectangular shape from alumina ceramic or the like to form a common electrode 4, a signal connection terminal 5, an individual electrode 7, and a ground electrode 8. is there. The drive ICs 6,. . . , 6 are arranged in a row.

More specifically, the signal connection terminals 5 are arranged in a row at the center 2a of the rear edge of the insulating substrate 2 so as to extend to the rear edge of the insulating substrate 2. Although the number of the signal connection terminals 5 is very small as compared with the conventional one,
This replaces the wiring that was conventionally done on the flexible substrate side,
This is because the process is performed using the signal system conductor pattern 5a on the insulating substrate 2. A part of these signal conductor patterns 5a is also shown in FIG.
6 is bonded to the pad 6a by a wire W.

The signal-system conductor pattern 5a is connected to the signal-system connection terminal 5, and DI, DO, LA
(Latch), CLK (clock) V _DD , and STR (strobe) 1-4. It is difficult to directly wire-bond the driving ICs 6 and 6 located at the center to the ground electrode 8 due to the arrangement, and therefore, dedicated ground terminals 5 (GND) are prepared.

Both ends of the common electrode 4 are formed so as to extend along the peripheral edge of the insulating substrate 2 and between both short sides of the insulating substrate 2 along the rear edge of the insulating substrate 2, respectively. Reaches the center 2a of the trailing edge of the insulating substrate and becomes the connection terminals 4a. The connection terminals 4a are assigned three conductor patterns 4b having the same shape as the signal system connection terminals 5, and are disposed on the left and right sides of the signal system connection terminals 5 along the longitudinal direction of the insulating substrate 2. Further, a silver paste 4c is applied to the connection terminal 4a in order to reduce the resistance value.

Reference numeral 7 denotes an individual electrode, and its tip 7
a is arranged so as to mesh with the comb tooth portion 4 d of the common electrode 4. The base end portion 7b of the individual electrode 7 is pulled out to the vicinity of the driving IC 6, and is bonded to the corresponding pad 6b with the wire W. The reason why the individual electrodes 7 are drawn obliquely is to allow a space between the driving ICs 6.

On the common electrode comb-teeth portion 4d and the individual electrode tip portion 7a, a heating resistor 3 of a pressure film is formed. The portion of the heating resistor 3 sandwiched between the comb teeth portions 4d, 4d corresponds to one dot. Of course, the heating resistor 3 can also be a thin film, and the design can be changed as appropriate. The ground electrodes 8, 8 are separated at the center 2a of the rear edge of the insulating substrate, and extend in the longitudinal direction of the insulating substrate 2 along the inside of the common electrode 4 from the center 2a toward both ends 2b, 2b. Is formed in a line. The connection terminal 8a of each ground electrode 8 has a conductor pattern 8b,. . . 8b are assigned to the signal system connection terminals 5 and disposed on both left and right sides along the longitudinal direction of the insulating substrate 2. Furthermore, the connection terminals 8a of the ground electrode 8 are provided with a lower resistance. Silver paste 8c is applied. Both ground electrodes 8, 8
Is the drive I, except for the two drive ICs 6 and 6 in the center.
C6,. . . , And 6 are wire-bonded to the GND pads. Note that the driving ICs 6. . . , 6 are coated with resin 9 and wires W,. . . , W together with insulation protection.

The thermal head substrate 1 is mounted on a heat sink 10. At this time, the thermal head substrate 1 is bonded only at the central portion 10c of the heat radiating plate. This is because the thermal head substrate 1 and the heat radiating plate 10 have different coefficients of thermal expansion. This is because the substrate 1 and the heat radiating plate 10 are freely expanded to prevent warpage.

The flexible substrate edge 11a overlaps the rear edge 2a of the insulating substrate, and is formed with a conductor pattern (not shown) for contacting and conducting with the connection terminals 4a, 5, 8a. As described above, since the signal connection terminals 5 are concentrated on the rear edge 2a of the insulating substrate, the width of the flexible substrate 11 (and the reinforcing plate 12) can be reduced. The flexible substrate 11 is reinforced by a reinforcing plate 12 as in the related art. A connector 14 is attached to the reinforcing plate 12, and a pin 14 a of the connector 14 is connected to a conductor pattern (not shown) on the flexible substrate 11.

The reinforcing plate 12 includes screws 17 together with the cover 15.
It is fixed to the heat sink 10 by a (see also FIG. 2). The screw 17a is inserted into the insertion hole 15a of the cover 15 and the insertion hole 13 of the reinforcing plate 12, and is screwed into the female screw hole 10a of the heat sink 10. At this time, the silicone rubber 16 on the bottom of the cover 15
Is the edge of the flexible substrate 11a at the center 2 of the rear edge of the insulating substrate.
a. The tightening torque of the screws 17a, 17a is controlled so that a uniform contact conduction state between the conductor pattern of the flexible board edge 11a and the connection terminals 4a, 5, 8a is obtained. In this embodiment, two screws 17a, 17
The pressure contact is performed only with the tightening force a, because the width of the flexible substrate 11 as described above may be narrow, and the screw tightening torque can be managed more easily than before.

A large-diameter insertion hole 15 is provided at both ends of the cover 15.
B is drilled, a spacer 18 is inserted, and a screw 17b is screwed into the female screw hole 10b of the heat sink 10 through the spacer 18 (see also FIG. 3).
Although the head of b is in contact with the cover 15, the fastening force of the screw 17b is applied exclusively to the spacer 18, and the biz 17b is configured to simply prevent the end of the cover 15 from floating. This is because if the end of the cover 15 is completely fixed to the heat radiating plate 10, there is a possibility that the whole will be distorted when the temperature rises due to the difference in the thermal expansion coefficient of each member.

In the thermal head of this embodiment, the voltage drop of the common electrode 4 is small at both ends of the thermal head substrate 1 and large at the center as in the prior art. However, the voltage drop of the ground electrode 8 is small at the center of the thermal head substrate 1 and large at both ends. Therefore, the sum of the voltage drop of the common electrode 4 and the voltage drop of the ground electrode 8 becomes
The thermal head substrate 1 becomes substantially uniform in the longitudinal direction. For this reason, the heat generation energy of the thermal head substrate 1 is made uniform, and unevenness in print density is eliminated.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a thermal head according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of the thermal head.

FIG. 3 is a fragmentary rear view showing the thermal head with a part thereof cut away.

FIG. 4 is a plan view of a principal part of a thermal head substrate of the thermal head.

FIG. 5 is an exploded perspective view of a conventional thermal head.

[Explanation of symbols]

 Reference Signs List 2 Insulating substrate 3 Heating resistor 4 Common electrode 4a Common electrode connection terminal 5 Signal system connection terminal 5a Signal system conductor pattern 6 Driving IC 7 Individual electrode 8 Ground electrode 8a Ground electrode connection terminal

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masato Sakai 21 Ryozaki-cho, Saiin-ku, Ukyo-ku, Kyoto Inside ROHM Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/335 B41J 2/345

Claims (1)

(57) [Claims] 1. An insulating substrate having a rectangular shape, a heating resistor formed parallel to a long side near one edge of the long side on the insulating substrate, and an edge of the one long side on the insulating substrate. A common electrode formed over the heating resistor and between both short sides thereof, and electrically connected to the heating resistor in common; an individual electrode formed on the insulating substrate to individually supply current to the heating resistor; A plurality of drive circuit elements provided on the insulating substrate and connected to the individual electrodes, a ground electrode formed on the insulating substrate and connected to each of the drive circuit elements, and a plurality of drive circuit elements formed on the insulating substrate and In a thermal head comprising various signal conductor patterns to be connected, the ground electrode is formed in the vicinity of the other long side edge of the insulating substrate so as to extend linearly in parallel with the long side, Line-shaped ground electrode In the middle, a divided portion is provided, and a connection terminal for connecting an external circuit to each of the various signal-system conductor patterns is provided at the divided portion so that each of the connection terminals extends to an edge of a long side of the insulating substrate. A thermal head characterized by being formed.